1. Field of the Invention
The present invention relates generally to an uplink scheduling method in a wireless system, and in particular, to a method of scheduling uplink resources for VoIP (Voice over Internet Protocol).
2. Description of the Related Art
A pressing need exists for a scheduling scheme to efficiently use resources in a wireless system that provides a variety of services with limited resources. It is ideal that unnecessarily allocated resources are quickly returned and re-allocated by scheduling. In addition, a technique for utilizing residual resource saved by reducing the data amount, for other purposes, can be considered.
There are many conventional uplink scheduling types for VoIP service.
Major examples are UGS (Unsolicited Grant Service) and rtPS (realtime Polling Service).
The UGS allocates uplink resources of a fixed size upon user request. The user then sends transmission data to a base station (BS) using the uplink resources. The rtPS allocates required resources in response to a periodic uplink resource allocation request from the user. Thus, the user sends transmission data using resources allocated corresponding to the amount of the transmission data.
FIG. 1 is a graph illustrating a conventional UGS-based uplink scheduling procedure.
Referring to FIG. 1, mobile status is divided largely into a talk-spurt period (ON) and a silence period (OFF) on a time axis. Transmission data packets exist in the talk-spurt period, whereas no transmission data packets exist in the silence period. In the illustrated case of FIG. 1, resources supporting a maximum rate (Rate 1) are fixedly allocated.
However, a subscriber station (SS) does not send data using all the allocated resources. Only minimum required resources (e.g. Rate ⅛) are used to maintain the service in silence periods 110 and 118.
Even in a talk-spurt period, only part of the allocated resources may be used. That is, the SS sends data packets using the allocated resources fully or partially in the talk-spurt period. For example, data packets are sent at Rate 1 using all the allocated resources in a talk-spurt period 112. On the other hand, data packets are sent at Rate ½ in a talk-spurt period 114 due to a decrease in the amount of transmission data. In a talk-spurt period 116, data packets are sent using no more than a quarter of the allocated resources. Then the SS uses the minimum resources in the silence period 118. The minimum resources are those supporting the minimum rate, Rate ⅛.
As described above, part of the fixedly allocated resources become residual resource in the periods 114, 116 and 118 using rates other than the maximum rate. This implies inefficient uplink scheduling. As a result, uplink resources are dissipated in the talk-spurt periods as well as in the silence periods.
FIG. 2 is a graph illustrating a conventional rtPS-based uplink scheduling procedure.
Referring to FIG. 2, the SS sends a resource allocation request to the BS in the rtPS, as indicated by reference numerals 212 to 236. The BS allocates requested uplink resources to the SS. The SS then sends data packets using the allocated resources, as indicated by reference numerals 210, 220 and 230.
There are three talk-spurt periods 210, 220 and 230 according to the data rates used. Data packets are sent at Rate 1 in the first talk-spurt period 210, at Rate ½ in the second talk-spurt period 220, and at Rate ¼ in the third talk-spurt period 230. Accordingly, the SS requests different amounts of resources in the talk-spurt periods 210, 220 and 230. Transitions from the talk-spurt period 210 to the talk-spurt period 220 and from the talk-spurt period 220 to the talk-spurt period 230 occur due to the decrease of data rate in the MS.
To be more specific, upon generation of data packets in a silence period, the SS requests resource allocation in step 212. The BS allocates maximum resources to support a maximum data rate (e.g. Rate 1). The SS sends data packets at Rate 1 using the allocated resources. The data transmission at Rate 1 is repeated in the talk-spurt period 210.
As the data rate changes due to the decrease in the amount of transmission data in the talk-spurt period 210, the SS requests resource allocation supporting a decreased data rate, Rate ½ in step 222. Then, the SS sends data packets using resources allocated by the BS. The data transmission at Rate ½ is repeated in the talk-spurt period 220.
If the data rate is to be further reduced in the talk-spurt period 220, the SS requests resource allocation supporting a decreased data rate, Rate ¼ in step 232. Then, the SS sends data packets at Rate ¼. The data transmission at Rate ¼ is repeated in the talk-spurt period 230.
After the data transmission is completed, the SS operates using minimum resources (e.g. Rate ⅛) in a silence period 240.
As noted from the above description, a periodic polling from the SS (i.e. uplink resource requests 212 to 218, 222 to 226, and 232 to 236) is required in the rtPS. Thus, even in the case where data packets are to be sent using the same resources as indicated by reference numerals 210, 220 and 230, the periodic polling 214 to 218, 224 to 226, and 234 to 236 is performed. The unnecessary polling leads to dissipation of uplink resources.
As described above, the UGS and rtPS allocate uplink resources periodically according to their scheduling types irrespective of real-time mobile status. That is, the time-variant mobile status is not reflected in real time in the uplink scheduling. Accordingly, a need exists for developing an efficient uplink scheduling scheme for reflecting mobile status in real time.